His chief accuser, Andrea Constand, bravely took the stand to publicly relay for a second time her recollection of the horrifying 2004 attack.

Constand, 45, a former Temple women's basketball administrator, told jurors that Cosby knocked her out with three blue pills he called "your friends" and then penetrated her with his fingers as she lay immobilised, unable to resist or say no.

It was the only criminal case to arise from a barrage of allegations from 62 women who have publicly said the former TV star drugged and molested them over a span of five decades.

Constand sat stone-faced in the first row but tilted her head back and breathed a sigh of relief after jurors were formally polled.

One of his victims, Lili Bernard, burst into tears as the verdicts were read, prompting Judge Steven O'Neill to call for order in the Montgomery County courtroom.

Cosby waved to the crowd outside the courthouse, got into a car and left without comment.

Cosby's lawyer Tom Mesereau, who won an acquittal for Michael Jackson on child-molestation charges, says the "fight is not over" and that his client planned to appeal the verdict.

The verdict was considered the first big celebrity trial of the #MeToo era, completing the spectacular late-life downfall of a comedian who broke racial barriers in Hollywood on his way to TV superstardom as America's dad.